The adoption of photovoltaics for generating electricity from sunlight is largely driven by cost considerations. At present, photovoltaic systems are not competitive with fossil-fuel generated electricity. Thus, there is a need to reduce the overall photovoltaic system cost. This entails reducing the costs associated with photovoltaic solar cell fabrication.
One way to reduce costs is to reduce the size of the photovoltaic solar cells. In this aspect, small and thin photovoltaic cells have been developed that reduce photovoltaic material use dramatically. These thin photovoltaic cells are typically formed on top of a handle wafer. Once formed, the cells may be individually detached from the handle wafer by, for example, an etching process using a hydrofluoric acid (HF) solution to undercut the cells. These “free floating” cells may then be assembled into sheets by attracting the individual cells to a desired position on a sheet of material using self-assembly techniques. Finally, the cells may be embedded in a low-cost substrate with contacts and microlenses to form photovoltaic sheets.
Although reducing the size of the solar cells helps to reduce costs, it may also reduce cell efficiency. Various cell configurations have therefore been developed in an effort to improve efficiency. For example, emitter wrap-through (EWT) cells are high-efficiency back-contact solar cells that include vias that allow an emitter on the front of the cell to be “wrapped-through” to the back surface. This type of cell can be fabricated with lower quality and thinner silicon without significant losses in efficiency. Another type of photovoltaic cell designed to improve efficiency is known as the point-contact-cell. The point-contact-cell has alternating n and p regions that form a polkadot array on the bottom surface and metallization to provide electrical contacts on the bottom surface. Such devices, however, only offer a limited set of possible improvements in cell efficiency.